I. Field of the Invention
The present invention generally relates to communication systems and, in particular, to systems and methods for medium access control on a wireless network.
II. Background Information
Currently, a data processor, such as a computer, can communicate over a wireless medium using a variety of protocols. One such protocol is defined by Wireless LAN [Local Area Network] Medium Access Control (MAC) and Physical Layer (PHY) Specifications, ANSI/IEEE Standard 802.11, 1999 (referred to herein as “802.11-1999”) and its supplements, such as Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Higher Speed Physical Layer Extension in the 2.4 GHz Band, IEEE Standard 802.11b, 1999 (referred to herein as “802.11b”). IEEE 802.11-1999 and its supplements are collectively referred to as “IEEE 802.11.” Using IEEE 802.11, a computer can send data to or receive data from another computer (or processor) over a wireless media.
FIG. 14 depicts an exemplary known wireless message exchange between two computers labeled A and B. Referring to FIG. 14, to send data, computer A first sends a Request To Send (RTS) message to computer B. If computer B receives the RTS message and is willing to accept data from computer A, computer B sends a Clear To Send (CTS) message over a wireless media (e.g., air) which forms a network. When computer A receives the CTS message, it responds by sending data to computer B. Computer B may then send an Acknowledgement (ACK) message once it has received the data sent by computer A. Computer B may further process the data locally or may forward the data to another network, computer, and/or processor. Moreover, the message sequence depicted in FIG. 14 may occur whenever computer A has data for computer B. Furthermore, computer B may initiate a similar message sequence by sending a RTS message to computer A. The message exchange thus serves to control access to the transmission medium. With the aforementioned message exchange, another computer (not shown) can interpose itself between computers A and B and intercept one or more of the messages exchanged between computers A and B. When this is the case, computers A and B are not exchanging messages. Instead, computers A and B are exchanging messages with the interloping computer. Moreover, computers A and B may not be aware of the disruption in communication and security caused by the interloping computer. This form of interloping may be accomplished even when computers A and B are encrypting their communications, e.g., by the interloper recording and playing back encrypted messages. Such forms of attack are sometimes termed “replay attacks.” Accordingly, systems and methods are needed that improve security and, in particular, provide a mechanism for protecting the media access control message sequence from disruption.